In a UMTS (Universal Mobile Telecommunications System) network, for the purposes of improving spectral efficiency and improving the data rates, system features based on W-CDMA (Wideband Code Division Multiple Access) are maximized by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access). For this UMTS network, for the purposes of further increasing high-speed data rates, providing low delay and so on, long-term evolution (LTE) has been under study (non-patent literature 1).
In a system of the LTE scheme, a MIMO (Multi Input Multi Output) system to improve the data rate (spectral efficiency) by transmitting and receiving data by a plurality of antennas is proposed (see, for example, non-patent literature 1). In MIMO transmission, a receiver selects optimal PMIs, from a codebook in which a plurality of amounts of phase/amplitude control (precoding matrices (precoding weights)) to be set in the antennas of a transmitter and a plurality of PMIs (Precoding Matrix Indicators) to be associated with the precoding matrices are defined on a per rank basis, and feeds the optimal PMIs back to the transmitter. Also, the receiver select and feeds back RIs (Rank Indicator), which represent optimal ranks, to the transmitter. The transmitter specifies the precoding weight for each transmitting antenna based on the PMIs and RIs fed back from the receiver, performs precoding, and transmits transmission information sequences.
Also, in a system of the LTE scheme, time domain/frequency domain/space domain scheduling relies on downlink channel conditions. Consequently, to allow the transmitter to perform optimal scheduling, the receiver reports the channel state. As parameters to report this channel state, there are the above PMIs, and downlink quality information (CQI: Channel Quality Indicator) for use in adaptive modulation/demodulation and coding process (AMC: Adaptive Modulation and Coding scheme). Scheduling is executed by feeding back these PMIs and CQI (channel state information (CSI) or feedback information) from the receiver to the transmitter.